Apparatus for integrating measurement of x-rays or radio-active rays



June 12, 1956 2,750,516

` J. P. AMBROSEN APPARATUS FOR INTEGRATING SUREMENT OF X-RAYS OR RADIO-ACT RAYS Filed June 50, 1952 147,1! 'lll/l l Il flllll/Illllllllllll Jou/w P AMBRosEN INVENTOR By WMI ATTORNEYS APPARATUS FR ENTEGRATING MEASUREMENT @F X-RAYS R Dill-ACTIVE RAYS Johan Peter Ambrosen, Gentofte, Denmark, assigner to Civilforsvarsstyrelsen, Copenhagen, Denmark Application .inne 30, 1952, Serial No. 296,363

Claims priority, application Denmark .lnne 30, 1951 Claims. (Ci. Z50-83.6)

The invention relates to an apparatus for integrating measurement of X-rays or radioactive rays, especially hard gamma rays', particularly a pocket apparatus for use for staffs working in fields infected with radioactive material, which apparatus is of the type having an ion chamber with at least two electrodes operating substantially at atmospheric pressure, two of said electrodes forming a condenser which with an additional parallel connected condenser, the insulating foil of which consists of a material with an extremely large specific electric resistance as e. g. polystyrol, polyethylene, polytetrauorethylene, or similar insulating materials, is charged to a given voltage and is discharged on account of the ionization in the apparatus.

lt is an object of the invention to provide an apparatus which in different ways is better than known apparatuses of the type in question.

The additional condenser used in the apparatus consists of alternative layers of insulating material and conductive material in the form of foils.

It has proved possible to produce condensers with a comparatively large time constant, viz. about 500 days. With a View to the manufacturing of cheaper apparatuses it would, however, be desirable to be able to make the time constant still larger.

A theoretical contemplation of the matter shows that it isv of no avail, as one might be led to believe, to use an insulating foil of a larger thickness, The fact is that the time constant T is determined by:

T=C R (1) where C is the capacity and R the leak resistance. To the resistance the following formula applies:

PXG

where p is the specific resistance of the material, a the distance between the condenser electrodes, and A the area of the electrodes.

To the capacity the following formula applies:

eXA C* 47rd where e is the dielectric constant.

If in the Formula l, R and C are substituted by their values derived from the Formulas 2 and 3, it appears that atent ric nevertheless increased by the application of more insulating material between the condenser electrodes, viz. if the increase in thickness is procured by two or more insulating foils being used placed on top of each other in layers. The increase of the time constant is considerable, said constant rising by a factor of about 10-15, so that time constants of the order of magnitude of 5000 days can be obtained.

A confirmed scientific explanation of this phenomenon is not yet available, but it may be assumed that the conductivity of an insulating foil is due to local irregularities in the grid structure in which the molecules of the material must be supposed to be disposed, and that the mounting of two layers of insulating material on top of each other will entail that the points, at which such irregularities occur, will not happen to be in line with each other. It is also possible that the air gap which, in spite of the fact that the insulating foils are placed on top of each other and are subjected to a certain pressure, is present between them contributes to the effect.

It is known per se to manufacture condensers with double or multiple insulating material, e. g. paper, between the condenser electrodes for the purpose of attaining a better guarantee against puncture. Here it is, however, the natural consequence of the larger thickness of the insulating material that is utilized, and this known property aimed at may as regards principle equally well be obtained by a single layer of insulating .material being used of the same thickness as the total thickness of the double or multiple layers of insulating foil. It is quite another matter when the property forming the basis for the present invention is to be utilized, viz. the extraordinary increase of the time constant, said increase being expressly conditioned by the fact that two or more layers of insulating material are used which, by the way, in order that the advantage should be of any practical importance must be an insulating material with a large specific electric resistance.

The exceptionally large time constant which it is according to the invention possible to give the apparatus creates the possibility of obtaining an especially cheap apparatus. This means that not only will it be possible to provide a few persons within the civil defence and the military defence with registrating apparatuses, but within a reasonable range it will be possible to provide larger groups of the population, contingently every single person, with such an apparatus.

The apparatuses, which should later on be used by the doctors as basis for a diagnosis', are to be supplied to the population in the charged and closed state in the case of imminent danger of attack, and as soon as it may be supposed that a group of people have been exposed to irradiation, deriving e. g. from an atom bomb, said persons are to report for examination, and on the basis of the state of discharge of the apparatuses said persons have carried a temporary diagnosis can immediately be made, after which the persons are to be divided into groups, e. g. three, viz. those who are not attacked at all, those who are slightly attacked, and those who are severely attacked.

To the persons of the first group applies that one may be sure that said persons are unhurt by irradiation.

To the two last groups applies that even if on account of the simple and cheap design of the apparatuses a discharge not deriving from irradiation, but perhaps from a leakage with resulting penetration of moisture into the apparatus should have occurred, this will only mean that said person must report for an examination that at the worst is unnecessary.

As regards the two last groups one has, however, the/ possibility of a relatively early re-control of the reading of the apparatus at the moment of control, as is has proved that not only the persons, but also the apparatuses become ill when exposed to a strong irradiation. The illness of the apparatus asserts itself by its time constant being reduced very considerably when the apparatus is exposed to an irradiation of a sufficiently strong nature. The reduction may e. g. amount to from about 5000 to between 1GO and 200 days and is therefore easy to observe within a reasonable time.

This means that even if a person whose apparatus has been out of order should to begin with be regarded as more severely attacked than is really the case, the ensuing control of the apparatus can with certainty reveal whether irradiation has taken place at all.

The invention is further explained in the following with reference to the accompanying purely diagrammatical drawing, wherein Pig. 1 shows an apparatus with an additional condenser in accordance with the invention on an enlarged scale,

Fig. 2 a similar apparatus in accordance with the invention intended for a smaller measuring range, and

Fig. 3 a quite simple apparatus according to the invention.

The apparatus in Fig. l consists of a cylindrical case 1 which as regards shape and size has some resemblance to a fountain pen and which can consist of conductive material, preferably aluminium or an aluminium alloy, or which may carry an electrically conductive layer. The case l or the conductive layer forms one electrode of the apparatus. The case 1 is closed at one end and encloses the ion chamber which is divided into two parts, 2 and 3, by a unit consisting of a centrally located rodor stick-shaped electrode i which is enclosed by a wound condenser 5, which is in turn carried by a metallic cylindrical ring 6, the outer cylinder surface of which is in contact with the inside of the case ll. The ion chambers i?. and 3 are bounded by cup-shaped parts 7 and 8 consisting of graphitised, thermo-plastic or thermo-hardenable material which serves for ensuring the highest possible wave-length independence. In the cup-shaped part 7 an aperture S is provided, through which contact can be made with the centrally located electrode 4 either for the charging of the apparatus or for the measurement of the momentary voltage of the latter which is a measure for the quantity of irradiation, to which the apparatus has been subjected since the charging.

The electrode 4 may consist of aluminium or electron metal or some other suited material. Its size must be so adapted that there is no risk of its getting in contact with the graphitised material 7, 3. A certain minimum distance must in other words be kept between the two electrodes, so that even a rather rough handling of the apparatus cannot entail wrong indications.

The wound condenser 5 may expediently be made in the way that the internal layer of metal foil is iirst wound a few times around the preferably circular-cylindrical electrode 4, after which two or more insulating foils, placed directly on top of each other, are wound once or several times around the electrode 4 together with the internal layer, after which the outer layer is finally wound around it together with the insulating foils and the internal layer. The internal layer is so much shorter than the insulating foils and the outer layer, when the Winding of the condenser is nearly completed, that the material of the inner layer rst gives out and next the insulating material, so that the wound condenser is enclosed by one or more turns of the material of the outer layer, whereby a good metallic contact is obtained between the outer layer and the bearing ring 6, which is expediently divided into two parts along a plane through the axis and secured the condenser by clamping between the two parts.

By the fact that the insulation of the wound condenser is used for insulating the two electrodes 1 and 4 from each other, extra insulating material is avoided which would entail increased losses; But it is, of course, within the scope of the invention possible to use a separate insulating material to keep the two electrodes il and 4 at a distance from each other, so that the wound condenser e. g. forms a separate unit filling out the chamber 2. The capacity of the condenser may be e. g. cm. or pf.

For the purpose of avoiding an unintentional discharge of the apparatus it may, if it is not completely closed, be provided with a special device, e. g. as the one shown to the left in Fig. 1. A displaceable Contact member l@ is provided which slides in an insulating disc lll contingently greased with vaseline. The contact member 1.@ has a disc-shaped head 12 with a tag 13 projecting from its rim, besides a centrally located sealing disc lll, e. g. of rubber. The Contact member itl with the sealing disc 1d is by a spring 15, which abuts in part on the insulating disc lll, in part on the head 12, pressed to the left in the figure and thereby closes an opening 1.6 in the case 1. When the apparatus is to be charged or read, the contact member is by a pressure on the sealing disc 1d and against the action of the spring 15 pressed to the right in the figure, after which an especially designed electrode, which is in connection with the charging current source or the measuring apparatus, is brought into contact with the tag 13 and through this with the electrode 4. insulating parts may be provided, e. g. shaped on the insulating disc ll, which prevent the contact member il@ from being pressed to the right in the figure and into abutment on the electrode l without having first been turned a suitable angle around its longitudinal axis. There may be many other embodiments of the device which is to prevent an unintentional Contact with the electrode 4; while at the same time a moistureetight sealing is maintained, and any optional known device of this type may be used in connection with the apparatus in accordance with the invention. lt may be pointed out that contact devices are known operated by magnetic influence from the outside, so that rst a turning motion and next an axial displacement of the apparatus must be performed in order to obtain the contact desired. The case l may then be completely closed.

Fig. 2 illustrates how the measuring range may in a simple way be reduced, which may be desirable if apparatuses with two diferent measuring ranges are to be Imanufactured, so that also very small irradiation doses can be registered. The apparatus corresponds completely to that shown in Fig. l apart from the fact that the electrode 4, which is provided with an elongation at either end, is, as is the case with the cup-shaped parts, made correspondingly larger. rl`he alteration from the embodiment shown in Fig. l into that shown in Fig. 2 entails no essential variation in the capacity, the capacity of the wound condenser 5 being supposed to be about 1000 cm. If by way of example it is supposed that the size of the air space in the design in Fig. l is 1.5 crn.3 and the measuring range 0-50 Roentgen, while the air volume is 7.5 cm.3 in the design in Fig. 2, the apparatus shown in the latter figure will have a measuring range of 0-10 Roentgen.

The invention is not limited to the examples shown purely diagrammatically. It may be mentioned that the case may have an optional outer shape, e. g. be spherical or lensshaped, and it may also be provided with suitable carrying means in the form of clips, pins, chains, straps, etc. The case may also be designed as a part of some other object which should be carried along at all events. Furthermore, the electrode i may be interrupted so that it does not directly itself extend through the wound con denser 5. Special insulating parts, if any, for the support of a wireshaped electrode 4 may have the form of a hub with spokes for ensuring the large time constant. The parts 10, lll, l2, 13, 1d, and 115 may be dispensed with, it being possible to charge and measure by direct contact with the electrode 4 or with a contact member connected electrically to the latter.

Thus the apparatus can be made more simple than shown in Figs. 1 and 2 and so cheaply that it is not necessary to consider its re-use, and special devices for the prevention of misuse by unintentional discharging, whereby should here be understood a discharge not deriving from an ionization, may therefore be dispensed with. The reduction in production costs attained hereby is considerable, which will appear from the fact that the number of component parts is reduced from twenty-odd to about three, viz. a condenser, a container, and a lid or some other, contingently multipartite closure. It must only be remembered that the measurement performed on the apparatuses for the purpose of the temporary diagnosis requires, if no electrometer is incorporated, that both of the electrodes of the apparatus become accessible, and for this purpose the apparatus may be designed in different ways.

There may by way of example in an aluminium case 1, Fig. 3, be incorporated a condenser 5, one electrode of which is in connection with the case, and the other electrode of which projects into the ionization chamber which is formed by the upper free end of the preferably cylindrical case which is closed with a lid 17, which in a suitable manner seals so as to be moisture-tight, e. g. by means of rubber packings. The aluminium case may, however, also be closed in advance with a rubber stopper covered by an aluminium cap. The condenser may be sustained between two narrowings in the wall of the case.

lf it be desired again to use the whole apparatus after it has once been used and has been controlled, it is expedient if the case can be opened without being damaged, e. g. by the removal of the cap and the stopper, if any. if, on the other hand, one would permit that damage or part damage be done, e. g. to the cap only, the measuring electrode to be led into the otherwise inaccessible condenser electrode may be so arranged as to perforate the lid or cap. The electrode may e. g. consist of a thin metal rod which is pointed at one end and enclosed by insulating material like the wood on a wood pencil, so that the insulating material prevents a short-circuiting between the two electrodes of the apparatus when the perforation has taken place, and the measuring electrode is led further in so as to contact the condenser electrode.

The mounting of the condenser in the case may e. g. be performed by cold shrinking, i. e. so that the condenser is cooled down to a very low temperature, e. g.- 180, and then very quickly is brought into the aluminium case where it will clamp itself on account of its own expansion.

In an advantageous embodiment of the apparatus the closure closing the container with the condenser to the surroundings consists of a flask which completely encloses the container and is closed with a lid or a cap which may consist of a caoutchouc diaphragm and a cap like a crowncork. It has proved that flasks of the type used for vaccine etc. are more resistant to shocks than a thin aluminium case. Within the scope of the invention, many other embodiments may be imagined, distinguishing themselves by simplicity and cheapness. The closure may by way of example consist of an ampulla which completely encloses the cylindrical metal container and is closed by fusing. In this case, both of the electrodes of the apparatus are inaccessible, and when the measuring is to be performed the ampulla, which usually consists of glass, mu-st be completely removed, it no special measures are taken to insert two measuring electrodes into the interior of the ampulla or flask, after the latter has been opened.

Even if the invention is described in connection with a wound condenser which must be regarded as preferable, it may, of course, be carried out in connection with any optional condenser equivalent thereto, i. e. a condenser with coverings placed between two or more layers of thin dielectric located directly on top of each other and which preferably project out beyond the rims of the coverings.

As example may be mentioned a fixed condenser with plane parallel covering-s.

As examples of applicable insulating materials may be mentioned polystyrol, polyethylene, polytetrauorethylene, or the materials sold under the trade marks Textolite 1422 or Rexolite 1422, and it may be added that amongst otherwise similar insulating material-s the material will be preferred in which a recombination occurs earliest after an ionization.

As a rule the atmospheric pressure should prevail in the interior of the apparatus, amongst other things because the increase of the measuring range aimed at can be obtained solely by means of the condenser built with dielectric foil. It is, however, Within the scope of the invention to vary the operation pressure, e. g. with a view to applying the apparatus for other purposes.

l claim:

l. An apparatus for integrating measurement of X-rays or radioactive rays, especially hard gamma rays, particularly a pocket apparatus for use in working within elds infected with radioactive material, comprising an ion chamber with at least two electrodes operating substantially at atmospheric pressure, two of said electrodes forming a condenser, an additional condenser connected to said condenser, the dielectric of said additional condenser comprising at least two superposed layers of insulating material of high specic resistance, said additional condenser thereby having a time constant exceeding considerably that of a similar condenser' of the same capacitance but having only one layer of the same insulating material with the same total thickness as that of the superposed layers of insulating material in the additional condenser.

2. An apparatus as claimed in claim l wherein the additional condenser has a time constant of the magnitude 0f 5000 days before being irradiated.

3. An apparatus as claimed in claim l wherein the additional condenser has a time constant which is more than ten times that of the said similar condenser.

4. An apparatus for integrating measurement of X-rays or radioactive rays, especially hard gamma rays, particularly a pocket apparatus for use in working within elds infected with radioactive material, comprising an ion chamber with at least two electrodes operation substantially at atmospheric pressure, two of said electrodes forming a condenser, an additional condenser connected to said condenser, the dielectric of said additional condenser consisting of a laminated insulating material of high specific resistance.

5. An apparatus for integrating measurement of X-rays or radioactive rays, especially hard gamma rays, particularly a pocket apparatus for use in working within elds infected with radioactive material, comprising a cylindrical electrode defining an air filled ion chamber, a central electrode centrally mounted in said chamber, an insulating bearing ring between said cylindrical electrode and said central electrode, and a condenser between said insulating bearing ring and said central electrode wound on -said central electrode and comprising a plurality of layers of metal foil and a plurality of layers of insulating material separating said layers of foil, said insulating material being laminated, whereby the time constant of said additional condenser is greatly increased.

References Cited in the ile of this patent UNITED STATES PATENTS 2,535,030 Balsbaugh Dec. 26, 1950 2,536,991 Wollan et al. Jan. 2, 1951 2,587,254 Victoreen Feb. 26, 1952 2,601,637 Rose et al June 24, 1952 

1. AN APPARATUS FOR INTERGRATING MEASUREMENT OF X-RAYS OR RADIOACTIVE RAYS, ESPECIALLY HARD GAMMA RAYS, PARTICULARLY A POCKET APPARATUS FOR USE IN WORKING WITHIN FIELDS INFECTED WITH RADIOACTIVE MATERIAL, COMPRISING AN ION CHAMBER WITH AT LEAST TWO ELECTRODES OPERATING SUBSTANTIALLY AT ATMOSPHERIC PRESSURE, TWO OF SAID ELECTRODES FORMING A CONDENSER, AN ADDITIONAL CONDENSER CONNECTED TO SAID CONDENSER, THE DIELECTRIC OF SAID ADDITIONAL CONDENSER COMPRISING AT LEAST TWO SUPERPOSED LAYERS OF INSULATING 